Well, that's kind of a natural consequence of selection pressures. Trying to make labels sound neutral when one end of a spectrum is preferred to the other inevitably leads to the Euphemism Treadmill - it's the same thing with "intelligence" vs. "idiocy" / "retardation" / "being special".

The fact is, in our culture, high Openness has clear social advantages over Traditionalism; high Extroversion has clear social advantages over Introversion; Conscientiousness has clear social advantages over Impulsiveness; and Stability has clear social advantages over Neuroticism. Change the culture, and the local optima might change, which will change the connotation of the terms - for example, Competitiveness might scan better in some places than Agreeableness.

Just like smart people are just "better" than dumb people, extroverts are just "better" than introverts, and stable people are just "better" than neurotics - at least in this environment.